This invention relates in general to solar collector devices and to solar heating and cooling systems employing such devices.
Solar heating has long been considered a source of energy. But solar heat collectors have had poor efficiency. They have not converted enough of the incident radiation to heat to warrant the cost of installation. Accordingly there has been limited use of solar energy, particularly for heating and cooling.
Solar radiation is converted into usable heat by flat plate solar collector elements. These collector elements include a metal plate, usually steel, aluminum or copper, which are painted black so as to absorb solar radiation. The metal plate is called an absorber plate. A first glass plate is spaced about two centimeters in front of this solar radiation absorbing surface thereby creating a dead air space which provides insulation from loss of heat off the front surface of the metal plate. A second glass plate is normally spaced another two centimeters from the first glass plate to create a second dead air space. In this fashion, convection currents at the front surface of the metal plate are minimized. These glass plate substantially increase the efficiency of operation of the solar collector element. They also reduce the amount of radiation incident on the metal plate.
As used herein, reference to the "efficiency" of the solar collector element or unit or module refers to the percentage of solar radiation incident on the solar collector element that is converted to usable heat.
In one type of solar heating system, the back surface of the metal absorber plate forms one surface of a chamber through which air is pumped. This air is heated by contact with the absorber plate. Since the air acts to cool the absorber plate this type of system is frequently called an air cooled collector type of solar heating system. The heated air is then used to heat any desired space such as the rooms of a building. In another type of solar heating system, called a water cooled collector type of system, water pipes are soldered to or otherwise permanently affixed to the back surface of the metal absorber plate. These so-called liquid cooled solar collectors heat the water which is then used to provide a hot water heating system.
A major object of this invention is to increase the performance of a solar collector, meaning specifically to increase the amount of heat transmitted to the fluid that is used to carry off heat from the absorber plate.
As used herein, the term "insolation" refers to the rate of solar radiation that falls on the surface of the collector element. Insolation is measured in calories/minute-cm.sup.2. An increase of insolation will improve the performance of the solar collector system. As indicated above, the term "efficiency" refers to a measure of the percentage of insolation which is converted to usable heat. Thus, an increase in insolation as well as an increase in efficiency will provide an improvement in the performance of a solar heating system.
Accordingly, it is a purpose of this invention to improve both the insolation and the efficiency of a solar collector.
A further purpose of this invention is to increase the performance of the solar collector to a point where the fluid being heated can readily be brought to a temperature (of at least 90.degree. C.) where the fluid can be used to power an absorption air conditioner, a Rankine cycle engine or the like.
The overall performance of the system can also be improved if the solar collector structure permits changing the elevation of the solar collector unit a few times a year in order to optimize its orientation to incident solar radiation and thus increase its average insolation. Accordingly, it is a further object of this invention to provide a solar collector unit sufficiently light in weight so that its elevation can be changed when required.
It is important that any increase in the performance of the solar collector occur in a solar collector design that does not greatly increase the cost of the collector or the cost of installation. Accordingly, it is a further purpose of this invention to provide an increase in the performance of a solar collector at a cost factor which reduces the unit cost of heat provided.